The present invention is directed to a ceramic susceptor with an embedded metal electrode for use in a deposition system. More particularly, the invention is directed to an aluminum nitride susceptor with an embedded molybdenum mesh electrode.
Chemical vapor deposition is a process to deposit a thin film layer onto a substrate such as a silicon wafer. In general, the substrate is supported in a deposition chamber which is held at a near vacuum, and the chamber and substrate are heated to a high temperature, e.g., 400.degree. to 600.degree. C. Deposition gasses are injected into the chamber, and a chemical reaction occurs to deposit the thin film layer onto the substrate. The thin film layer may be a dielectric material (such as silicon nitride or silicon oxide) or a metal (such as tungsten), and the deposition may be plasma-enhanced or thermally enhanced. For example, for a dielectric chemical vapor deposition, to deposit a silicon nitride thin film, silane (SiH.sub.4), ammonia (NH.sub.3), and nitrogen (N.sub.2) gasses are introduced into the chamber, whereas to deposit a silicon oxide thin film, silane, oxygen (O.sub.2), and nitrous oxide (N.sub.2 O) gasses are introduced into the chamber. To deposit a tungsten thin film in metal chemical vapor deposition, tungsten hexaflouride (WF.sub.6) and hydrogen (H.sub.2) are introduced into the chamber. In a plasma-enhanced chemical vapor deposition process, the gasses are subjected to intense radio frequency (rf) electric fields, and a plasma envelopes the substrate to increase the rate of deposition of the thin film layer.
During the deposition process, other parts in the chamber, in addition to the substrate, may be coated by the thin film layer. The continued accumulation of such thin film materials on these parts may degrade the performance of the deposition chamber. Therefore, the chamber must be cleaned periodically. Typically, the chamber is cleaned after each processing run, i.e., each time the substrate is removed from the chamber. Alternately, the chamber is cleaned after two, three, or four processing runs.
Cleaning is conducted by injecting gasses containing highly reactive elements, particularly fluorine, into the chamber, and the chamber is maintained at a high temperature, e.g. 400.degree. C. to 600.degree. C. Cleaning gasses that may be used include carbon tetraflouride (CF.sub.4), nitrogen triflouride (NF.sub.3), and dicarbon hexaflouride (C.sub.2 F.sub.6). Oxygen or nitrous oxide may also be introduced into the chamber to prevent the formation of fluorocarbon polymers such as teflon which would otherwise degrade the clean process. The fluorine reacts with any thin film material that has been deposited on the mechanical parts in the chamber and strips off this material. During the cleaning process, the combination of the high temperature and reactive gasses create an extremely hostile environment inside the deposition chamber. Mechanical parts in the deposition chamber, are subject to corrosion and thermal stress fractures.
A susceptor (sometimes called a chuck) is a mechanical part that holds the substrate in the deposition chamber. In addition, the susceptor may act as an electrode, such as a DC or rf electrode. Conventional susceptors may be formed of aluminum with an anodized surface layer. Unfortunately, these anodized aluminum susceptors react with the fluorine gas and the anodized layer flakes off. As the anodized layer flakes off, the properties of the deposited film, such as stress, uniformity, and particle count, drift until out of specification. The susceptor must then be replaced. The typical lifetime of an anodized aluminum susceptor is two to four thousand processing runs, so the anodized aluminum susceptor needs to be replaced every one or two months.
In view of the foregoing, there is an unfulfilled desire for a susceptor with an embedded electrode which is highly resistant to the environment in a deposition chamber.